1. Field of the Invention
The present invention relates to a liquid crystal display device.
2. Description of the Related Art
In liquid crystal display devices including a sidelight-type backlight, light incident on the edge surface of a light guide plate is reflected at an interface on the back surface side, returns therefrom, and exits from the front surface (JP 2009-276531 A). Specifically, peak-shaped convex portions or valley-shaped concave portions are formed on the back surface side such that the ridge line extends in a direction orthogonal to a traveling direction of the light, and the light reflected by the convex portions or the concave portions exits from the front surface. Light traveling through the light guide plate includes, in addition to the light reflected at the interface on the back surface side, light passing through the back surface. For returning the passing light to the light guide plate, a reflective sheet is arranged.
In recent years, a reflective sheet having a high reflectance is sometimes used, which causes a problem that the light that should be reflected at the interface on the back surface of the light guide plate is absorbed by the reflective sheet because the reflective sheet is in close contact with the light guide plate. Moreover, the reflective sheet that is in close contact with the light guide plate expands with the thermal expansion of the light guide plate. However, when the light guide plate contracts, there arises a problem that the reflective sheet does not return to its original state and suffers from waviness.
As measures against these problems, it is conceivable to render the back surface of the light guide plate rough to thereby reduce its adhesion to the reflective sheet. However, the fine shape of irregularities constituting the rough surface is likely to reflect light at a short wavelength. Therefore, a phenomenon occurs in which blue light at a short wavelength first exits at a place close to a light source, and yellow or orange light at a long wavelength exits later at a place distant from the light source. Especially in a thin light guide plate or a large light guide plate, a difference in chromaticity is increased between the place close to the light source and the place distant therefrom. Moreover, most of light exits before reaching the place distant from the light source. Therefore, a difference in luminance also occurs in which a luminance at the place close to the light source is high and a luminance at the place distant from the light source is low.